The present invention relates to a probe device, which comprises at least one carrier arm mounted rotatably about a rotational axis, at least one probe connected to the carrier arm, and at least one cable guide for the guidance of a probe cable. The invention further relates to a rotating head having at least one such probe device and having at least one probe cable guided in the cable guide, and to a test apparatus having at least one such probe device or having at least one such rotating head.
In particular for the examination of semifinished products for faults, such as cracks and shrink holes, by means of eddy current or magnetic leakage flux methods, test apparatuses which are configured as rotating systems are employed. In such rotating systems, probe devices are disposed on rotatable rotating heads of the test apparatus. Since the rotating head, together with the probe devices disposed thereon, is rotated while an elongate test piece is pushed through a middle passage opening through the rotating head, the probe devices move relative to the test piece on a helical path. In order to be able to detect changes in the magnetic field resulting from flaws in the test piece, probes of the probe devices, which probes are intended for the eddy current method, must be located at a predefined distance, or as close as possible, to the surface of the test piece. In the magnetic leakage flux method, on the other hand, the probes are in contact with the test piece and drags on its surface.
A probe device or a probe carrier for a test apparatus, configured as a rotating system, for the non-destructive testing of an elongated test piece by means of leakage flux or eddy currents is known from DE 10 2012 108 241 A1. The probe carrier is of modular and plug-in design, so that the test apparatus can be rapidly adapted to a changed test piece diameter.
Other known probe devices have a carrier arm mounted such that it is freely movable about a pivot point. At one end of the carrier arm mounted in the manner of a two-sided lever is arranged the probe, and at that end of the carrier arm which lies opposite said first end is provided a counterweight. Insofar as a test piece moves for instance irregularly through the passage opening of the rotating head, the probes, owing to the rotatable mounting of the carrier arm that bears them, can take appropriate evasive action. By means of the counterweight and a spring that acts on the carrier arm, a position of the probe at a predefined distance from the surface of the test piece, and, where appropriate, a contact pressing force of the probe onto the test piece, given a predefined rotation speed of the rotating head and a predefined diameter of the test piece, can be adjusted.
In order that, in the case of large test pieces and correspondingly high rotation speeds of the rotating head, the probes do not lift off from the surface of the test piece, whereby the testing operation in the magnetic leakage flux method is interrupted, there is in practice a tendency to configure the spring force, and hence the contact pressing force of the probe onto the test piece, excessively high, or to reduce the rotation speed of the rotating head. A large contact pressing force leads, however, to increased wear of the probes dragging on the test piece surface, while a reduction of the rotation speed of the rotating head leads to a reduced throughput of the test piece. Also the correct adjustment of the distance of the probes from the surface of the test piece in the eddy current method generally proves difficult in practice, due to the influences of rotation speed and test piece diameter. A further influence is also exerted by probe cables, which run as cable bows or loops from a port or inlet on the rotating head to the probe device and, guided in a cable guide of said probe device via a carrier arm of the probe device, to the probe, in order to ensure the mobility of the carrier arm. Upon rotation of the rotating head, these cable bows experience a centrifugal force and thereby exert a torque on the carrier arm, whereby they influence the contact pressing force or the position of the probes in relation to the test piece.